Thin Film Transistors (TFT) in which oxide semiconductors are used can be used in LSIs or similar CMOS circuits. For example, a TFT in which an amorphous oxide semiconductor including indium (In), gallium (Ga), and zinc (Zn) is used has gathered attention. In the manufacturing process of a semiconductor device including a CMOS circuit, in, for example, a final process, a heat treatment (hydrogen sintering) in an atmosphere containing hydrogen is performed. In some cases, as a result of the hydrogen sintering, the resistance of the oxide semiconductor is lowered and the characteristics of the transistor are degraded. Therefore, an oxide semiconductor with stable electrical characteristics is desirable.